Spectrophotometry is the study of electromagnetic waves in the visible, near-ultraviolet, and near-infrared spectra. A spectrophotometer is a light measuring device that is configured to measure various characteristics of light, including intensity, color, and/or wavelength. Spectrophotometers have a wide range of uses. For instance, they may be used to detect colors on display devices such as televisions, projectors, monitors, and camcorder viewfinders. Alternatively, spectrophotometers may be used in printing devices to calibrate the colors printed.
Typically, when used as a color detector, the spectrophotometer may include a light source, a light collector, such as a photodiode, and a filter. In one instance, the light is projected toward an object. The object reflects the light, and the photodiode receives the reflected light. The light may pass through the filter before being received by the photodiode so that the color may be detected. Specifically, the filter is configured to only allow light having a specific range of wavelengths to pass through. Light that passes through generates current in the photodiode. This current indicates that the specific color of light is present. An array of photodiodes and filters allow for the spectrophotometer to receive more detailed information. For example, an array of 20 photodiodes each having a filter tuned/designed to filter light at different wavelengths would be able to discriminate between more colors than a system with fewer photodiodes.
While useful in many technology areas, spectrophotometers have several problems. For instance, the filter may include two metal films. However, the metal film may begin to oxidize after being exposed to air. The oxidization of the metal film reduces the net internal reflectance from the metal coating altering the performance of the filter as it degrades. The main effect of the reflectance degradation is to widen the bandwidth of the filter for a given transmission peak of the filter. This will reduce the color discrimination of the filter array as the filters overlap one another more in wavelength. Another problem for Silicon based photodiode systems is that certain wavelengths of light are difficult to detect. This is especially true for the blue region of the color spectrum. In order to compensate for this, some spectrophotometers amplify these colors electrically with an amplifier in order to make them more easily detectible; however, the amplifier also amplifies noise received by the sensor. The increased noise may lead to inaccurate readings by the light collector.
Accordingly, a spectrophotometer or color detector is needed having an improved filter and/or allow for color amplification without amplifying noise.